Ebikes – dual battery management system – first rides

I have waterproofed both the DBMS and the power meter, so am feeling a bit happier about going out for a ride or two.

I did my first ride just after I finished the basic unit, but it was all a bit short and hilly to get a grip on what was happening. I had a “dead spot” where power to the motor stopped for a few seconds, so wasn’t sure what was happening after that. However, I did 10-12km, and used power from both batteries, so something was working.

Today I went out with both batteries fully charged, the trip reset, and the power meter reset. Unfortunately, at the moment I have no data logging set up, nor do I have anyway of being sure which battery is attached at any instant. On steep hills, the new battery does suffer from more voltage drop, but normally the differences and the change overs are so subtle, I have no idea which battery is in use. Additionally, there is a good chance that at the point the processor decides to test the battery voltages I will be using no power, so the system may well stay on the same battery! Only when the first battery has been used enough to take the voltage below the second battery can we guarantee a battery change.

The power meter is excellent, easily readable even with polarised sunnies on, clear read out of volts, amps and watts, and 2 second scrolling through all the other various highs, lows and AmpHours and WattHours readings. In particular, the “uptime” is quite useful, I can work out when the next battery change might happen.

Start voltage on the 13Ah bottle battery was 40.72V, and on the 15Ah headway battery was about 40.2V.

I did 21.2Km, I was  moving for 62 minutes, and the DBMS was turned on for 69mins.

The whole system used 4.66Ah, or 171.8Wh. Peak amps was 14.97, Peak Watts was 551W. Lowest voltage recorded was 33V. Possible a connection not made properly, or a problem with the switch over algorithm.

At the end, Bottle battery was at 38.71, and Headway was at 39.76.

At the finish, the system was switched onto the headway battery, probably because the bottle battery had dropped below the voltage of the Headway. On a short ride like this one, balancing battery usage is not likely, but double the distance and we may start to see more equal usage of the batteries.

I got a couple of “dead spots” but I still have no idea what is causing it, some serious thinking and analysis required. The low voltage of 33V that was recorded may be some part of the problem.

I am not going to charge the batteries or reset the trip or Powermeter, so the figures may get more meaningful on the next trip.

The watt meter on the King Meter display unit from Lekkie was inaccurate most of the time, reading between 30W and 100W high. Even the battery bars indicator bore little relationship to the actual voltage being recorded.

Eventually, I would like to detect the ampage within the DBMS, and calculate watts and WattHours, and use these to make a more sophisticated battery switch algorithm, and also add a data logger to record volts, amps, time and battery selected, which I could analyse in a spreadsheet. This may help with ironing out the small issues.

Soon, maybe. 🙂



Posted in Arduino, Dual Battery Management System, Electric Bikes, Programming, Yuba Mundo eV4

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